Analysis of the stimulated Brillouin scattering threshold of coupling ring-assisted multi-mode fiber

In order to reduce inter-mode crosstalk, a coupling ring-assisted multi-mode fiber structure was proposed, and the mathematical model of its excited Brillouin scattering gain spectrum was established. Theoretically, the excited Brillouin scattering threshold of the coupling ring-assisted multi-mode fiber was analyzed, as well as the effects of fiber parameters and modes on the excited Brillouin scattering spectral threshold. The results show that the coupling ring-assisted structure increases the effective refractive index difference to 1.75 times that of the conventional type step-index multi-mode fiber. The threshold of the excited Brillouin scattering spectrum in coupling ring-assisted multi-mode fiber follows the increase of the fiber length from a sharp decrease to a slow one and finally converges to a constant value of 30 dBm at 18 km, which is higher than that of the conventional step refractive index multi-mode fiber. Other things being equal, the threshold increases linearly with the attenuation coefficient, the effective cross-sectional area of the fiber core, and the mode order of the fiber; it increases exponentially with the increase of the core radius. This study provides a theoretical reference for enhancing the transmission distance and channel capacity of fiber optic communication systems.